Microwave transition elements



Jan. 13, 1959 R. I. HARRISON ET AL MICROWAVE TRANSITION ELEMENTS Filed Feb. 15, 1956 INVENTORS RICHARD l. HARRISONB: LEFLER Mc KEE ATTORNEY MICROWAVE TRANSITION ELEMENTS Richard Harrison, Mineola, N. Y., and Letler McKee, Mountain View, Calif, assignors to Sylvania Electric Products Inc, acorporation of Massachussetts Application February 15, 1956, Serial No. 565,589

14 Claims. (Cl. 333-21) ditions, a microwave transition element is used to connect the first and second guides together. This element serves to transfer the energy between the two guides and at the same time to transform the energy from the first mode to the second mode. Ideally, the energy transfer should take place with no losses; there should be no energy reflection between the two guides. Further, this transfer should be efiiective over a wide or broad band range of operating frequencies.

One particular problem of energy transfer and trans,- formation is presented by the necessity of transferring energy between a ridged waveguide and a helical waveguide, as for example, When the helical waveguide element of a travelling wave tube is to be connected to a rectangular or circular ridged waveguide. These guides have different dominant modes. For example, at relatively high microwave frequencies, the dominant mode of the ridged guide is normally the TE mode while that of the helical guide is normally the h (FUND) mode. (The TE mode terminology is conventional, whereas the h (FUND) mode terminology follows that established in the article Travelling Wave Tubes, published in Advances in Electronics and Electric Physics, vol.

As far as it is known to us, there is no microwave transition element now in existence that can operate efiectively at all microwave frequencies extending upward for example into the millimeter range of wave lengths. We have invented a microwave transition element which can be used for this purpose.

Accordingly, it is an object of the present invention to provide a new and improved microwave transition element for transferring microwave energy between a helical waveguide and a ridged waveguide.

Another object is to improve microwave transition elements interconnecting ridged waveguides and helical waveguides in such manner that these elements can be used effectively over a wide range of microwave frequencies.

Still another object is to provide a new and improved microwave transition element interconnecting a helical waveguide to a single or double ridged rectangular or circular waveguide in such manner as to provide efiicient microwave energy mode transformation.

United States Patent O Patented Jan. 13, 1959 energy between rectangular or circular ridged waveguides and helical waveguides.

These and other objects of our invention will either be explained or will become apparent hereinafter.

In accordance with our invention we provide a ridged waveguide (for example of the circular or rectangular type) which, when an incident electromagnet wave is Yet another object is to efficiently transfer microwave supplied thereto, establish a first dominant mode therefor. The ridged guide is provided with at least one ridge. This ridge has a cut out portion. The boundary wall of the cut out portion describes an open curved path (i. e. the wall does not close upon itself) which extends between first and second Walls of the ridge. The ridged guide is further-provided with an orifice which communicates between the outer surface of the ridged guide and the cut out portion of the ridge.

We further provide a helical waveguide (for example of the regular or non-regular helical types) which, when said incident wave is supplied thereto, establishes a second dominant mode therefor. The helical guide extends through the orifice into the cut out portion. One end of the helical guide is positioned within the cut out portion. The'helical guide is provided with an extension element which is coupled between said one end and the first ridge wall.

The curvature of the boundary wall is such that the separation between the helical guide and the boundary wall varies from point to point along the periphery of the helical guide. For example, the wall curvature can describe an exponential or spiral function.

When said incident wave is supplied to one of these guides, it will be found that this wave propagates into the other waveguide in a substantially loss free manner. The energy mode transformation occurs under bilateral matched conditions and there is no energy reflection in either guide. Further, this transformation is effective over an inherently broad frequency band.

Our invention will now be described with reference to the accompanying drawings wherein:

Fig. 1 illustrates one embodiment of our invention employing a single ridged rectangular waveguide; and

Fig. 2 illustrates a second embodiment of our invention employing a double ridged rectangular waveguide.

Referring now to Fig. 1, there is provided a rectangular waveguide 9* which has a ridge 12 terminated bya first ridge wall 14 spaced from and parallel to the guide wall 16. For this single ridged waveguide 9, a major portion of the dominant mode power appears between the first ridge wall 14 and the narrow confronting band 16a of the wall 16.

The ridge 12 is provided-with a cut out portion 28, the boundary wall of which is designated by the numeral 28a. This boundary wall extends in an open curved path (that is a path which does not close upon itself) between the first ridge wall 14 and a second ridge wall 16b which lies substantially in the plane of the wall 16 as a continuation of the strip 16a.

A helical waveguide 24 arranged concentric of axis 26 extends through an orifice 22 in a side wall 20 of waveguide 9 into the cut out portion. One end 23 of the helical guide is positioned within the cut out portion. An extension element 21 connects this one end 23 to the first ridge wall 14. l

The curvature of the boundary wall 28a (which for example, can be defined by a spiral or exponential function) is such that the separation between the periphery of the helical guide and the boundary wall varies from point to point along the helical guide periphery. This separation is comparatively large in the region denoted by the numeral fatl and graduallydecreases to gated therein.

In the region 30, the helical periphery-boundary wall separation. is relatively large, and the helical guide establishes the dominant mode (the h (FUND) mode) for the propagated energy. In the region 32, this separation is relatively small and the field configuration is substantially identical with the dominant mode of the rigid. guide. in the regions intermediate to regions 34 and 32, the separation gradually decreases and the energy in the h 'CEUND) mode is gradually transformed to energy'in the TE mode.

The element 21 serves as a substantial continuation of the first ridge wall 14, and the boundary wall 28a in the region 32 forms a gradual transition into the second ridge wall 16b lying in the planeof guide wall 16. By

appropriate design, energy transmission to and from the helical waveguide may be achieved in principle with no loss and under matched conditions.

The described transition may also be used with round wire helices (instead of the tape or ribbon helix shown) by gradually tapering the cross-section of the element 21 from a round cross-section at end 23 into a tape or ribbon before connection to the ridge wall 1. Alteratively, the round wire can be connected by element 21 to a'ridge wall, which is likewise rounded such as to create no discontinuity. The round ridge then can be tapered to a rectangular ridge such as that described above.

The ridged rectangular waveguide 9 can be replaced by a ridged circular waveguide and the entire structure will still function in the same manner.

'Moreover, more than one ridge can be used as shown in Fig. 2. Here, a double ridged rectangular waveguide 100 having anupper ridge Hi2 and a lower ridge 12 is used to replace the single ridged waveguide of Fig. 1. The cut out portion 1494 now is formed in such manner that its boundary wall extends between the first ridge wall 14 and a second ridge wall 104 of ridge 102. This arrangement'is otherwise identical with that shown in Fig. l and will operate in the same manner.

While we have shown and pointed out our invention as applied above, it will be apparent to those skilled in the art that many modifications can be made within the scope and sphere of our invention as defined in the claims which follow.

What is claimed is:

1. In combination, a ridged waveguide, the waveguide ridge having first and second ridge walls and a cut out portion, the boundary Wall of said portion describing an open curved path extending between said first and second walls, said ridged guide being further provided with an orifice communicating between the outer and inner surfaces :of the ridged guide; and a helical waveguide extending through said orifice into said out out portion, one end of said helical guide being positioned within said out out portion, said helical guide being provided with an'extensionelement coupling said one end to said first ridge wall.

27 The combination as set forth in claim 1, wherein the path has a degree of curvature at which the separation between the boundary wall and the periphery of said helical guide varies from point to point along said periphery.

' 3. The combination as set forth in claim 2-, wherein the axis of said helical guide is perpendicular to the axis ofsaidridged waveguide.

4."In"conibination, a ridged waveguide responsive to an incident electromagnetic energy having a given microwave frequency range to establish a first dominant mode therefor, the waveguide ridge having first and second ridge walls and a cut out portion, the boundary Wall of said portion describing an open curved path extending between said first and second walls, said ridged guide being further provided with an orifice communicating between the outer and inner surfaces of the ridged guide and a helical waveguide responsive to said incident energy to establish a second dominant mode therefor, said helical guide extending through said orifice into said out out portion, one end of said helical guide being posit oned within said cut out portion, said helical guide being provided with an extension element coupled between sald one end and said first ridge wall, said path hav ng a curvature at which the separation between the per meter of the helical guide and the boundary wall var es from point to point along said periphery, said variation in separation establishing a dominant mode transformation between both guides at which when said energy is supplied to one guide, said energy propagates through the other guide in a substantially dissipationless manner characterized by the absence of wave reflections.

I 5. The combination as set forth in claim 4, wherein said ridged guide is a rectangular guide.

6. The combination as set forth in claim 4, wherein said ridged guide is a circular guide.

7. The combination as set forth in claim 4, wherein sai curvature is defined by an exponential function.

The combination as set forth in claim 4, wherein said curvature is defined by a spiral function. 9. In combination, a ridged rectangular waveguide having first and second mutually orthogonal pairs of parallel guide walls, the waveguide ridge extending between the walls of said first pair, said ridged guide having a first section in which each of two opposite walls of said ridge are flush with the corresponding wall of said first pair and having a second section in which one of said ridge walls is spaced apart from the corresponding wall of said first pair, said ridge in a region common to both sections having a cut out portion, the boundary wall of said portion terminating in said second section at said one ridge wall and terminating in said first section at the wall of said first pair flush with said one ridge wall, one wall of said second pair having an aperture; and a helical waveguide extending between said aperture and said cut out portion, one end of said helicalguide being positioned within said cut out portion, said helical guide being pro vided with an extension element connecting said one end to said one ridge wall in said second section. V

10. In combination, a ridged rectangular waveguide having first and second mutually orthogonal pairs of par allel guide walls, the waveguide ridge extending between the walls of said first pair, said ridged guide having a first section in which each of two opposite walls of said ridge are fiush with the corresponding wall of said first pair and having a second section in which one of said ridge walls is spaced apart from the corresponding wall of said first pair, said ridge in a region common to both sections having a cut out portion, the boundary wall of said portion in said second section having a first termination substantially integral with said one ridge wall and in said first section having a second termination substatially integral with the wall of said first pair, one wall of said second pair having an aperture; and a helical waveguide extending between said aperture and said cut out portion, one end of said helical guide being positioned'within said out out portion, said helical guide being provded with an extension element coupled to said one end and having a termination substantially integral with said first termination of said boundary Wall.

11. The combination as set forth in claim 10, wherein the axis of said helical waveguide is perpendicularto the axis of said ridged waveguide.

aaeaoea 12. The combination as set forth in claim 11, wherein the boundary wall has a curvature at which the separation between the helical waveguide and the boundary wall established in said first section is smaller than the separation between the helical guide and the boundary wall established in said second section.

13. The combination as set forth in claim 12, wherein the boundary wall has an exponential curvature.

14. In combination, a ridged rectangular waveguide having first and second mutually orthogonal pairs of parallel guide walls, the waveguide ridge extending between the walls of said first pair, said ridged guide having a first section in which said ridge is an inte ral unit extending between the walls of said first pair and is in contact therewith and having a second section in which said ridge extends between the walls of said first pair and is in contact therewith but also is provided with a slot extending parallel to both of said guide wall pairs, said slot being defined by first and second opposed separated ridge walls, said ridge in a region common to both sections having a cut out portion, the boundary wall of said portion terminating at one end at one ridge wall and termi mating at its other end at the other ridge wall, one wall of said second pair having an aperture, and a helical waveguide extending between said aperture and said out out portion, one end of said helical guide being positioned within said out out portion, said helical guide being provided with an extension element connecting said one end to one of said ridge walls.-

Reterences Cited in the file of this patent UNITED STATES PATENTS 2,660,667 Bowen Nov. 24, 1953 FOREIGN PATENTS 1,075,546 France Apr. 14, 1954 

